The present invention relates to an electronic musical instrument employing a waveform memory and generating musical tones based on waveform data stored in the memory.
Conventional electronic musical instruments are known which employ a waveform memory storing waveform data corresponding to musical sounds of non-electronic musical instruments such as piano or organ. Waveform data of each waveform are digital data which define the amplitudes of the waveform and consist of a fixed bit-width word. The waveform memory is implemented by memory devices which have a plurality of storage areas each one capable of storing a fixed bit-width word, and which allow reading of data word-by-word. The bit-width of the memory devices is determined based on the bit-width of the waveform data to be stored. For example, when the bit-width of the waveform data is 12 bits, a memory device with an 8-bit-width, and a memory device with a 4 bit-width are employed as the waveform memory. Alternatively, three memory devices, each one of which is a 4-bit-width may also be employed as the waveform memory.
It is necessary to store waveform data corresponding to many kinds of waveforms in the waveform memory in order to implement electronic musical instruments capable of generating many kinds of musical tones having different tone colors. In considering the bit-width of the waveform data, the preferable bit-width is about 16 bits when storing the waveform data of percussive sounds such as piano sounds because the regeneration of these sounds requires a high S/N (Signal/Noise) ratio and a large dynamic range. In contrast, the regeneration of sustained sounds such as an organ sound does not require such a high S/N ratio. Therefore, it is no problem to make and store the waveform data of the sustained sounds at 12 bit-width. Thus, the preferable bit-width of the waveform data is different in accordance with the waveforms of the musical sounds. In conventional electronic musical instruments, however, all waveforms are coded into digital data having a same bit-width and the digital data are stored in the waveform memory for regeneration of musical sounds. Therefore, the following problems occur:
(1) In the case where the bit-width of the waveform data is small, the bit-width does not satisfy the requirement for the regeneration of the musical sounds which are to be regenerated at a high S/N ratio and at a high dynamic range so that the corresponding sounds cannot be regenerated at a high sound quality. PA1 (2) Conversely, when the bit-width of the waveform data is large, although the sound quality is high, all the data including the musical sounds which do not require the regeneration at a high S/N ratio and a high dynamic range and which do not require such a large bit-width are also stored. In this case, the large storage areas are occupied by unnecessary bits, and such a wasteful use of storage areas is un-economic and is not appropriate for electronic musical instruments. PA1 a waveform memory for storing waveform data which are obtained by sequentially sampling musical tone waveforms, the waveform memory having a plurality of storage areas each of which is capable of storing a piece of data of a fixed bit-width, in which in the case where the bit-width of the waveform data corresponding to a musical tone waveform is different from said fixed bit-width, the whole waveform data corresponding to the musical tone waveform are stored in the waveform memory so as not to generate vacant memory areas and the waveform data may be divided if necessary and the parts of the waveform data obtained by the division are stored in a plurality of neighboring storage areas of the waveform memory; and PA1 a tone generator for reading out the data stored in the waveform memory corresponding to a desired musical tone to be generated, and for determining the waveform data from the read out data based oil the bit-width of the waveform data of the desired musical tone, and for generating the musical tone based on the determined waveform data.